Objective  To understand the urinary fluoride level and changes in bone biochemical metabolism indexes among workers exposed to ammonium bifluoride and to explore bone metabolism biomarkers in ammonium bifluoride-exposed workers.

  Methods  Totally 74 workers occupationally exposed to ammonium bifluoride in a semiconductor and liquid crystal panel production enterprise (as an exposed group), as well as 70 workers in a nearby electronic factory (as a control group), were studied. The urinary fluoride, serum osteocalcin, serum alkaline phosphatase, and urine hydroxyproline were measured, and the differences between these two groups were compared.

  Results  The airborne concentrations of hydrogen ammonium bifluoride (calculated as hydrogen fluoride) in the workplaces of the studied plant varied from non-detectable (lower than 0.014) to 0.021 mg/m³, which were lower than the national occupational exposure limit. Seven workers in the exposure group had excessive fluoride values in their pre-shift urine samples, with an excessive rate of 9.45%. There was a positive correlation between the urinary fluoride values of workers in the exposure group and the airborne concentration of hydrogen fluoride (r=0.332, P < 0.05). The urinary fluoride mass concentration of workers in the exposure group (0.69 ±0.77) mg/L was higher than that of the control group (0.47 ±0.17) mg/L, and the difference was statistically significant (P < 0.05). The serum osteocalcin concentration of workers in the exposure group (15.07 ±3.68) ng/mL was lower than that of the control group (16.51 ±4.51) ng/mL, and the difference was statistically significant (P < 0.05). There was no significant difference between the serum alkaline phosphatase concentration (76.99 ±14.99) U/L of workers in the exposure group and that of the control group (75.03 ±22.35) U/L (P > 0.05). The urine hydroxyproline concentration of workers in the exposure group (1 134.01 ±145.34) μmol/L was higher than that of the control group (721.30 ±138.31) μmol/L, and the difference was statistically significant (P < 0.01). If the workers were grouped according to their urinary fluoride level, those with higher urinary fluoride values than 1.0 mg/L had higher urinary hydroxyproline values than those of those with lower urinary fluoride values (> 0.5 - 1.0 mg/L and > 0 - 0.5 mg/L) (P < 0.05).

  Conclusions  Urinary fluoride and urine hydroxyproline may be sensitive biomarkers of bone metabolism in workers exposed to ammonium bifluoride.